Modern welfare states compete with private providers of welfare in offering economic security. This is most evident in the case of pensions competing with life insurance and private pensions as well as of public health insurance competing with private insurance providers. The common view of this public–private relationship is one of a trade-off: longitudinally, political scientists describe how retrenchment was pushed by privatized welfare, whereas economists trace the crowding-out of private to public welfare provisions. Cross-sectionally, they claim that countries have lower public spending levels because they have a large private sector. We suggest a more nuanced view. Drawing on a new long-run panel data of public pension and private life insurance expenditures and contributions in 20 OECD countries since Bismarck to the current day, we show that in the postwar years a cross-sectional trade-off emerged, which then faded. Longitudinally, complementary relationships of public and private provision growth have become the norm. We argue theoretically and show empirically that trade-offs only occur if governments still hold (waning) anti-interventionist and pro-market views.